Pokémon X and Y are the first Pokémon games introduced into Generation VI. The games were announced through Nintendo Direct by Satoru Iwata on January 8, 2013.
Pokémon X and Y have featured entirely new gameplay, that differs to past Pokémon games, as both have a complete 3D game play experience.

Contents

Gameplay

The gameplay in Pokemon X and Y is slightly different from past games. Game Freak has added Sky Battles, and Horde Battles.
This game also different points of view too. It is usually to show off the capabilities of the 3DS.
Triple Battles, and Rotation Battles make a return from the 5th Generation also.
Super Training is a new addition to the series. It makes calculating IVs, and EVs easier, to show off the true potential of your Pokemon.
Pokemon Amie is a feature that allows you to "hang out" or play with your Pokemon. You can feed them, make faces, and play minigames. (Pokemon Amie and Super Training are both accessed through the bottom screen of the 3DS. Use the L/R buttons to switch between them)

The two biggest changes added to the series is the introduction of the Fairy-type, and Mega Evolutions.
The fairy-type was added to balance the type chart a little more, according to Game Freak.
Dragon, Dark, and FIghting are all weak against it. While Steel, and Poison are super effective against it.

Mega Evolutions are basically battle-only evolutions that make your Pokemon stronger for a limited time. Some Pokemon's mega evolution affects the original typing, stats, and ability. Check the list below about all of the Mega Pokemon.

Multiplayer

The multiplayer aspect of Pokemon has always been large. Well, Game Freak to it a step further by adding Wonder Trade. It is a option in the PSS. (Player Search System) It allows you to pick one of your Pokemon and trade it to random person anywhere in the world.
Battles have also been changed. Now, you can communicate with three other people in the world and have a 2-on-2 player match.

Pokemon Bank is a cloud-service Nintendo is offering to let players transfer their 5th Generation Pokemon and store them online. It is $5 a year and you can only access it though a Nintendo Network ID.
A free trial is being given out for the first month after it's release. Using the bank allows to get an Event Celebi.

Plot

This game is about you, Serena/Calem, (depending on your gender) and three other friends as you journey through the Kalos region. While along the way you learn about Mega Evolution and stopping Team Flare's bad deeds!

New Pokémon

A total of 72 new Pokémon have been discovered in the Kalos region, bringing the total number of Pokémon up to 721.

Mega Evolution

A new concept introduced to the games is Mega Evolution, which allows certain Pokémon to evolve past their final forms temporarily. This will cause these Pokémon to take on new appearances, sometimes changing their type, as well as allowing them to possess new abilities. Only one Pokémon can evolve during battle, and must be holding their respective Mega Stone. Not all Mega Stones can be collected through the main game however. After entering the Hall of Fame, you must talk to Professor Sycamore in Anistar City, and this will allow the player to find the remaining Mega Stones. These particular stones can only be found between the hours of 8 PM-9 PM.